5,双折射 Double Refraction
1) 双折射现象
unpolarized light
自然光
O光
e-光
双折射 双折射 双折射
calcite
方解石
The,double-bending” of a beam transmitted
through calcite,is called double refraction,
2) the ordinary ray (O-ray) and the extraordinary
ray (e-ray).( 1687年惠更斯研究)
a) two beams are polarized light with their planes
of vibration at right angles to each other,
c on s tn
r
i
o ??
0
0
s in
s in
O光
e光
b) O-ray obey the refraction law,
The crystal has a single index
of refraction no,
c) The e –ray index of
refraction varies with
direction from no
to a smaller value
(for calcite) ne,
c o n s tin
r
i
e
e
e ??? )(
s in
s in (与入射角有关 且不为定值)
对 O光,
对 e光,
(与入射角无关
且为定值)
e光在晶体中传播,
光速是一变值。 nvCri ??s ins in为什么?
自然光 方解石
3) optic axis 光轴
78o
78o 68o
102o
a) optic axis 光轴 ---
光轴
The direction at which a
beam transmitted through
calcite without double
refraction called optic axis,
b) The optic axis is found
by erecting a line at
either of the two corners
where three obtuse angles
meet (the,blunt, corners),
making equal angles 68o with the crystal edges,
Any line in the crystal parallel to this line is also
an optic axis,
光轴
4) principal section 主截面
The principal section is
consist of the normal to
crystal surface and optic
axis,
?Any section in the crystal
parallel to this section is
also the principal section,
注意,
?when incident ray lie in the principal section,the vibration of O-ray normal to the principal section
and the vibration of e-ray parallel to the
principal section,
?n?
102o
78o
78o
78o 光轴
?入射面在主截面内时,o光 e光的振动面互相垂直
Two planes of vibration at right angles to each other,
且 o光为振动面垂直
于主截面的偏振光;
e光为振动面平行于
主截面的偏振光;
?n?
5)正晶体与负晶体
Positive crystal and
negative crystal
oe nn ?? 也可可以
Negative crystal,ne < no
oe vv ?? 也可可以
Positive crystal,ne > no
78o
78o
?n?
6)用惠更斯原理解释双折射现象
evv ?0
因 O光沿各向传播的速度是相同的,故 O光的波面是球面。
而 e光在晶体内沿各向传播的
速度不相同,所以 e光的波面
是椭球面。
正晶体 --
负晶体 -- evv ?0
在晶体内一个点波
源发光的波阵面,
78o
光轴
正晶体 负晶体
o光
e光
光轴
(负晶体) incident ray lie in the principal section,
A) There is a angle between optic axis and crystal surface
光轴与晶体表面有一夹角(正入射 )
自然光
optic axis
光轴
B) optic axis is parallel to the crystal surface
光轴与晶体表面平行(正入射)
自然光
o光 e光
光轴
O e 二光通过厚度 d的光程差,dnn
oe )( ???
4/?? ? 2/?? ?四分之一波片
二分之一波片(半波片)
结论,
evv ?0 enn ?0
有双折射。
自然光
o光 e光
光轴
C) optic axis is normal to the crystal surface
光轴与晶体表面垂直(正入射)
(负晶体) 无双折射现象
o光 e光
晶体
光轴 光轴
D) There is a angle between optic axis and crystal surface
光轴与晶体表面有一夹角(斜入射)
A’ A
B CC’
7) polarizing prism 偏振棱镜
自然光
光轴
68o 71
o
W·Nicol prism 尼科尔棱镜( 1928年)
no=1.658
ne=1.486 o光
e光
N加拿大 =1.550
O光以 76o入射到 加拿大 树胶,产生
全反射后被吸收。
76o
?70
6 5 8.1
5 5 0.1a r c s in ??
临介i
e光出射成为偏振光
A’
C’
Calcite
方解石
A
D
C
B


光轴
o光
e光
O光
e光
eo vv ?
eo vv '' ?
Wouaston prism
渥氏棱镜 光轴
o光
e光
when incident ray lie in the
principal section,the vibration of O-ray normal to the principal
section and the vibration of e-
ray parallel to the principal
section,
n
v
C
r
i ??
s in
s in
O,e二光通过晶体
后被分得很开,从
而获得偏振光。
8) Applications of polarization 偏振光的应用
汽车车灯与窗玻璃用同一偏振化方向的透明膜
a) 防止对面来的灯光耀眼
2)放立体电影
原理:利用人眼的双眼效应
作业,